1. Field of the Invention
The present invention relates to a method of forming a color image by an electrophotographic system, an electrostatic recording system etc. More particularly, the present invention relates to a method of forming a color image by which graininess, color reproducibility and smoothness are not deteriorated, offset to fixing roll does not occur, and high glossiness can be uniformly reproduced on a transfer material without depending on image density.
2. Description of the Related Art
Conventionally, a color image is formed on a transfer material, e.g., when a color copy is obtained, by an electrophotographic system in such a manner as described below. Namely, light is applied to an original, then the reflected light is separated into colors by a color CCD (charge coupled device), is subjected to image processing by an image processing apparatus and to color correction so as to obtain image signals of multiple colors. The image signals are converted into laser light modulated by using, e.g., a semiconductor laser for each color. The laser light is irradiated on an inorganic photosensitive material, such as selenium (Se) and amorphous silicon, or an organic photosensitive material in which a phthalocyanine pigment, bis-azo pigment, etc. is used for a charge generating layer a plurality of times, with one color at a time so as to form a plurality of electrostatic latent images. The plurality of electrostatic latent images are developed sequentially by using, e.g., four color toners of Y (yellow), M (magenta), C (cyan) and K (black). The developed toner images are then transferred from the inorganic or organic photosensitive material onto a transfer material such as paper, and are heated and fixed thereon by a heat-fixing roll or the like. As a result, a color image is formed on the transfer material.
Meanwhile, in the above-described case, the color toner is, for example, prepared by adhering inorganic fine particles such as silicon oxide, titanium oxide and aluminum oxide or resin fine particles such as PMMA (polymethyl methacrylate), PVDF (polyvinylidene fluoride), having an average particle size of, e.g., 5 to 100 mm, to particles having an average particle size of, e.g., 1 to 15 mm prepared by dispersing a colorant in a binding resin such as polyester resin, styrene/acrylic copolymer and styrene/butadiene copolymer. The above-described colorants include, e.g., bendizine yellow, quinoline yellow and hanza yellow as the Y (yellow), rhodamine B, rose bengal and pigment red as the M (magenta), phthalocyanine blue, aniline blue and pigment blue as the C (cyan), carbon black, aniline black and blends of color pigments as K (black).
Since the surface of the color image by color toners formed as described-above is made smooth during heat-fixing processing, it has a glossiness which is different from that of the surface of a paper. Further, it has been known that the viscosity of the color toner during the heat-fixing processing varies depending on the kind of the binding resin contained in the color toner and the type of heat-fixing system, and that the glossiness of the color image thereby varies.
Although the desired level of glossiness of a color image varies and is different depending on the kind of image, the use to be made of the image, etc., an image having a high glossiness is preferred from the viewpoint of obtaining clear images in the case of a photographic original such as human figures and landscapes. For examples, Japanese Patent Publication No. 5-142963,A, No. 3-2765,A and No. 63-259575,A disclose that an image having a high glossiness is obtained by using a color copying machine and selecting the toner materials and fixing conditions, etc. However, in the case of these techniques described in the publications, although the glossiness of the image area with toner can be increased, the glossiness of a non-image area cannot be increased and the glossiness on a transfer material cannot be uniform.
In order to address the above-described problems, methods of transferring and fixing a transparent toner in addition to color toners to a transfer material are proposed in Japanese Patent Publication No. 63-58374,A, No. 4-278967,A, No. 4-204670,A, No. 5-232840,A No. 7-72696,A. However, the amount of developed transparent toner is not controlled sufficiently with these methods.
An object of the present invention is to address the various problems in the above-described references. Another object of the present invention is to provide a color image forming method and a color image forming apparatus by which an image having a high glossiness can be reproduced uniformly on a transfer material without deteriorating the graininess, color reproducibility and smoothness of the image, and without any occurrence of offset to a fixing roll and without depending on image density.